Field of the Invention
The present disclosure generally relates to a cutter assembly for cutting a tubular in a wellbore.
Description of the Related Art
A wellbore is formed to access hydrocarbon bearing formations, for example crude oil and/or natural gas, by the use of drilling. Drilling is accomplished by utilizing a drill bit that is mounted on the end of a tubular string, such as a drill string. To drill within the wellbore to a predetermined depth, the drill string is often rotated by a top drive or rotary table on a surface platform or rig, and/or by a downhole motor mounted towards the lower end of the drill string. After drilling to a predetermined depth, the drill string and drill bit are removed and a section of casing is lowered into the wellbore. An annulus is thus formed between the string of casing and the formation. The casing string is temporarily hung from the surface of the well. The casing string is cemented into the wellbore by circulating cement into the annulus defined between the outer wall of the casing and the borehole. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons.
It is common to employ more than one string of casing in a wellbore. In this respect, the well is drilled to a first designated depth with the drill string. The drill string is removed. A first string of casing is then run into the wellbore and set in the drilled-out portion of the wellbore, and cement is circulated into the annulus behind the casing string. Next, the well is drilled to a second designated depth, and a second string of casing or liner, is run into the drilled-out portion of the wellbore. If the second string is a liner string, the liner is set at a depth such that the upper portion of the second string of casing overlaps the lower portion of the first string of casing. The liner string may then be fixed, or “hung” off of the existing casing by the use of slips which utilize slip members and cones to frictionally affix the new string of liner in the wellbore. If the second string is a casing string, the casing string may be hung off of a wellhead. This process is typically repeated with additional casing/liner strings until the well has been drilled to total depth. In this manner, wells are typically formed with two or more strings of casing/liner of an ever-decreasing diameter.
From time to time, for example once the hydrocarbon-bearing formations have been depleted, the wellbore must be plugged and abandoned (P&A) using cement plugs. This P&A procedure seals the wellbore from the environment, thereby preventing wellbore fluid, such as hydrocarbons and/or salt water, from polluting the surface environment. This procedure also seals sensitive formations, such as aquifers, traversed by the wellbore from contamination by the hydrocarbon-bearing formations. Setting of a cement plug when there are two adjacent casing strings lining the wellbore is presently done by cutting a window in each of the adjacent casing strings and squeezing cement into the windows to provide a satisfactory seal. A tool designed to cut through casing requires different cutter properties than a tool designed to section mill a casing. It would be advantageous to combine the different attributes onto a single tool. There is a need for a more effective apparatus and method of cutting casing/liner in the wellbore.